Incorrect Function message Remote Desktop into Vista

Trying to remote desktop into Vista using the updated Vista Client on
XP.

I get to my box alright, and see the Vista blank screen, its attempting
to login then I get:

a little red box
and the message "incorrect function" displayed on the vista screen,
with an "OK" button.

Click OK and Remte Desktop window closes, taking me back to the RDP
login window on the calling machine.

Any ideas what "Incorrect Function" means?

The only thing I see in the Application Log of the destination box is:
Source: Winlogon
EventID: 6003
Message: The winlogon notification subscriber <TrustedInstaller> was
unavailable to handle a critical notification event.

Any ideas?